In this type of damping force variable damper, oil flows through ports formed in a piston, and damping force is created by the resistance when the oil flows. To vary the damping force, it is common to vary the amount of oil flowing through the ports to change the damping force.
An example of this type of vehicle damper of variable damping force is a damper in which an electromagnet is used to suitably open and close the ports and the damping force of the damper is varied, as is disclosed in Japanese Patent Application Post-Exam Publication No. 1-47323 (JP 01-047323 B), for example.
The damper of variable damping force of JP 01-47323 B will be described below with reference to FIG. 10 hereof.
A conventional damper 500 of variable damping force shown in FIG. 10 is configured from a tubular cylinder 501, a piston 502 slidably mounted in the cylinder 501, damper oil (not shown) that flows through the interior of the cylinder 501 via a plurality of ports 503 formed in the piston 502, a rod 504 that is attached to the piston 502 at one end and that protrudes at the other end to the outside of the cylinder 501 via a rod guide (not shown), a valve 505 that is attached to the piston 502 coaxially with one end of the rod 504 and that opens and closes the ports 503, 503, and an electromagnetic solenoid (electromagnet) 506 provided to the piston 502 for driving the valve 505.
However, in the aforementioned damper 500, since the valve 505 is attached coaxially to the piston 502, it is impossible to obtain sufficient distance from a supporting part (fulcrum) 507 of the piston 502 to opening/closing parts (points of force) 508, 508 of the ports 503. Therefore, it has been difficult to impart flexible movement to the valve 505. Since the valve 505 is highly rigid, there have also been many cases in which force is needed to open and close the valve 505. Therefore, the valve 505 has had a slow response speed, and it has not been possible to appropriately control the valve 505. The valve 505 has also lacked durability because the valve 505 is highly rigid.
Furthermore, in the damper 500 of variable damping force, the opening/closing end of the valve 505 is separated from the piston 502 when the valve 505 is in an open state. To move the valve 505 from an open state to a closed state, a magnetic circuit is formed by the piston 502, the valve 505, and the electromagnetic solenoid 506 when an electric current is run through the electromagnetic solenoid 506. However, when the valve 505 is separated from the piston 502, the magnetic flux of the magnetic circuit has a smaller surface area than in cases in which the valve 505 is firmly affixed to the piston 502. Therefore, when the valve 505 is returned from the open state to the closed state against the flow of fluid (damper oil), there have been many cases in which sufficient return force cannot be created in the valve 505 and the responsiveness of the valve 505 is reduced.